Optical flame detectors are old in the art of providing automatic detection of fires. A feature shared by all such optical detectors is a shield window so that dust, soot or oil cannot be directly deposited on the optical detectors. Optical detectors are known to provide broad or narrow frequency detection of infrared and/or ultraviolet range frequencies. For instance, a typical hydrocarbon fire will typically have detectable peaks in the wavelengths of 2.7 and 4.3 micrometers. Ultraviolet radiation, though typically emitted at low levels, is detectable by way of on optical detector for an appropriate frequency range.
A flame detector, which is a type of fire detector having a fast detection response, is configured such that the light receiving element of the flame detector detects the specific wavelength bands of ultraviolet (UV) rays and infrared (IR) rays radiated from a flame, generated when a fire first originates, and detects the generation of the flame at the start of a fire using electronic characteristics that light energy is converted into electrical energy. Prior art flame detectors cannot cope with a deterioration in sensitivity when a monitoring window is covered with dust or the like, thus resulting in flames not being detected. While the prior art includes measurement of such deterioration of sensitivity based upon electronic detection and measurement of a later covered shield window as compared with a clean shield window, once a signal strength is reduced to below a minimum level required for detection of flames by the IR or UV sensors, due to fouling of the shield window or presence of smoke associated with the fire, no amount of signal compensation in the prior art flame detector systems will matter. The flames simply will not be detected.
U.S. Pat. No. 8,346,500 describes a common structural requirement and limitation of prior art flame detectors, i.e., in FIG. 6 is shown a sensing angle of sensors. That sensing angle is a simple consequence of requiring a housing and shield window above the support board for the IR and UV detectors. IR and UV signals passing through that sensing angle are not in the prior art captured or focused in any enhanced manner other than having the signal waves impinge upon the shield window and be transmitted through it to the IR or UV detectors below the shield window.
Such a structure is a limitation because signal waves that impinge upon the housing adjacent to or beyond the shield window are simply reflected into space and are unavailable to the sensors, where if such reflected signals were capable of being delivered to the sensors with the signals presently in the prior art sensing angles of flame detectors, a greater range of signals weakened by smoke, other physical obstacles, or fouling of the shield window would then result in positive detection of flames. The prior art has failed to provide a structure or method by which the range of detection of existing IR or UV sensors can detect flames because of the above described physical occlusion, small size of the flames, or a substantial distance between the flame and the flame detector, all situations in which IR or UV signals reaching the sensors can fall below detectable levels.
Optical sensors convert incoming IR and/or UV radiation into electrical signals, which are then preferably converted to digital signals for evaluation by comparison and alarm microprocessors to determine whether fire or flame is present in the space that can be detected by the sensors. It is well known that weak signals reaching the sensors result in a low signal to noise ratio so that a level of undetectability is reached. If that signal to noise ratio could be increased, the flame detectors' performance would improve in two ways: stronger signaling from flames could result in detection of flames and the flame detector would be much more immune to false alarms. The conventional method of increasing signal to noise ratio for incoming optical signals to optical sensors is to attempt improvement in sensor technology and/or signal processing for signals within a noisy environment. The current state of the art in flame detectors is directed solely at these two efforts to improve performance of flame detectors.
Even so, there is a need for provide a structure or method by which the range of detection of existing IR or UV sensors can detect flames because of the above described physical occlusion, small size of the flames, or a substantial distance between the flame and the flame detector, all situations in which IR or UV signals reaching the sensors can fall below detectable levels.
It is to these ends that the present invention has been developed.